1. Field of the Invention
The present invention pertains to vapor collection, and in particular to the collection of condensable vapor from a carrier gas.
2. Description of the Related Art
In many commercial processes, it is desirable to recapture vapors of volatile materials. U.S. Pat. No. 4,424,680, for example, teaches a method of recovering condensable vapors using liquid nitrogen. The liquid nitrogen is introduced into a carrier gas, thereby cooling the volatile material contained therein, which is sought to be recovered. The volatile material condenses into a liquid form which, as taught in U.S. Pat. No. 4,424,680, can be recovered using conventional means. However, it is clear from subsequent experience that the separation of a liquefied volatile component from a carrier gas cannot be attained at commercially attractive production rates. That is, the separation efficiency is so low as to preclude the economic recovery in certain commercial applications. In effect, U.S. Pat. No. 4,424,680 assumes that the separation of a liquefied volatile component, present as a mist in a carrier gas, is a simple and straightforward matter, to be handled with conventional demisting apparatus. Such approaches have been found to be impractical with moisture laden streams of an organic solvent or carrier gas because of the hydrate formation on a demister pad surface, and the hydrate's freezing on the mesh pad surfaces which blocks flow through the separation portion of the system.
Further, U.S. Pat. No. 4,424,680 is prohibitively expensive to operate in certain commercial installations because of the temperature control which must be maintained in two separate insulated vessels. Two separate vessels are required, according to the patent, to form three distinct processing zones, two zones for condensation and the remaining third zone for separation of the mist from the product path.
Another example of vapor recovery is given in Great Britain Pat. No. 2,098,874 which teaches an arrangement for condensing vapor evolved from a volatile liquid into the ullage space of a storage vessel, using two cryogen-cooled vessels.